Method of producing a photocell assembly



June s, 1965 w. HUGLE ETAI. 3,187,414

METHOD OF PRODUCING A PHOTOCELL ASSEMBLY v Filed Feb. 5, 1959 2 Sheets-Sheet 1 ||IIII @www l 1Il UUUUUUUUUUUD UDUUUUUUUUUUU Y June 8, 1965 w. B. HUGLE ETAL 3,187,414

METHOD OF PRODUCING A PHOTOCELL ASSEMBLY Filed Feb.- 5, 1959 2 sheets-sheet 2 FME- 7 115.54 y F115- Q from a reference axis.

United States Patent() 3,187,414 METHOD E PRODUCNG A PHTCELL v 1 ASSEMBLY William B. Hugle and Frances B. Hugle, Union Township, Clermont County, Ohio, assignors to D. H tldwn Company, (Jiucinnati, Ohio, a corporation of `Filed Feb. 5, 1959, Ser. No. 791,400 8 Claims. (Cl. 259-15562) t 'Thepresent invention relates to photocells and methods of manufacturing photocells. This application is a continuation-impart of application Serial No. 574,804, entitled Semi-Conductive Films and Methods of Producing Them,led March 29, 1956, now Patent No. 2,- 994,621.

In recent years, optical encoders have been developed.

which employ an assembly of photocells in combination with a light source'and a code disc disposed between the light source and photocell assembly to produce a binary output representing the angle of the code disc Application Serial No. 631,818 of Willi-am Pong entitled Encoder, filed December 31,

, 1956, now Patent No. 3,076,959, isan example of such an encoder. As pointed out in the Pong application, the sensitive areas of each of the photocells are desirably extremely small in order to avoid the use of ya readout slit between thecode disc and the photocell assembly. Y

` Although the `present invention will be illustrated as applied to an optical encoder, it is to be understood that photocell assemblies have many utilities in addition to optical encoders, such asdevices for reading out inform-ation on punched cards.

The present inventors have disclosed in their application referred to above the method of making the semiconductive lm by the steps vof depositing on the .electrically insulating base films` of anion material and cation material, and thereafter heating the superimposed lms to produce a reaction between .the anion and cation mateteristics and make it possible to use any of the well known circuit printing techniques for placing the electrode pair .on the substrate,.however, Vit has not always been possible to, reproduce photocells which exhibit the'same electrical characteristics. Further, the effective gap or slit width, that is the eiective distance between4 the confronting electrodes has proven to be greater in some constructions than the actual dista-nce between the electrodes, and the eitective slit varies from photocell to photocell. Y

It is believed that one ofthe causes of both the deviation-between the effective slit width and the actual slit width and the poor reproducibility of photocells is corrosion between lthe electrodes and the photoconductive layer. During-the process of forming the photoconductive layer-upon the electrodes from alternate lms of anion and cation material, relatively high temperatures are employed, and` it is believed thatcorrosion'products develop between the semiconductive layer and the electrodes during this step of the manufacturing process which introduce substantial resistance between the photoconductive strip and the electrodes.

. lt is also believed that the effective gap width of photocells of this type is in partinfluenced by the thickness of the photoconductive coating. This diculty can be solved by optical masking, that is providing an optical slit confrontingthe mass of photoconductive material.

lt is a further object of the presentinvention to provide a photocell using a .photoconductive lm on a substrate and electrodes disposedon the iilm to form an optical mask as well as electrical connections.

Further, the photocells which have previously been.

known and used have been relatively diicult to assemble and relatively expensive.

terminal. Photocell assemblies for use in encoders must be constructed with very small spacings between adjacent photocells, hence necessitating a relatively large number of terminals for the photocell in a very restricted area.

Further, it is desirable to employ printed circuittechni-1 lques forencoders due to the limited space, and hence the photocell terminals Iare preferably adapted tol plug into la printedcircuit board. It is, therefore, among the objectsl of the'present invention to provide a photocell and an assembly of photocells which may be more readily manufactured and at lower cost. k l These and additional objects of the present invention will be more readily appreciated from a consideration of the remainder of the disclosure, particularly when viewed in the light of the drawings, in which: p

FlGURE 1 is a sectional view'of a portion of an optical encoder employing a photocell assembly constructed according to the teachings of the present invention; A

FIGURE 2 is a-sectional view of the photocell assemi bly taken along the line 2 2 of FIGURE l;

FEGURE 3 is a sectional view ot' the photocell assembly taken along the line 3--3 of FIGURE 2;

FIGURES 4, 5, and 6 are plan views of masks employed in the process of manufacturing the photocell assembly andillustrated in FIGURES l through 3;

FIGUREK7 is a modified form of the mask of FIG- URE 4;

FIGURE 8 is a fragmentary sectional view taken along the line S-eg of FGURE 3; and

FIGURE 9 is atragmentary-sectional view of a modil ed form of photocell taken along the same yplane as FIGURE 8. v

As'illustrated in FGURE 1, the optical encoder has a` code disc 10 which is secured to a shaft vl2 and rotatable therewith. A light source 14 confronts the code disc 10, and includes a lamp 16 with an elongated lament 18. A photocell assembly 20 is mounted on the side of the disc 1lb opposite the light source 14, and includes a plurality of photocells 22 disposed with their lsensitive areas parallel to a radius lof the disc 10 and aligned with the light source 14.'` The filament 18 of the light source.

is normal to the axis of the sensitivel areas of the photocells 22 to approach a pointsource. A semicylindrical lens 24 is mounted to a transparent plate 26 with its ilat surface abutting the plate, and the lens is disposed between the phot-@cells 22 and the disc 10. The semicylindrical lens-24 is aligned with the light source and the photocells, and focuses the` light source on the sensitive areas of the photocells 22 in the manner disclosed in the patent application ofY William Mahaney entitled Optical Encoder, Serial No.V 627,456, tiled December l0, 1956, now Patent No. 2,941,088, issued June 14, 1960.

The photocell assembly 2li employsia glass disc 28 and a plurality of K-ovar pins 30 extend through the glass plate normal thereto and adjacent to the periphery thereof. The pins 30 are equally spaced from each otherthroughout an arc of approximately`240 degrees, and one pin 32 is disposed adjacent to the periphery of the disc approximately on the bisector of the subtended angle. A

Patented June 8, 1965 i This has partly been due to the difficulty of connecting each of the electrodes to a Kovar ring 34 is sealed about the periphery of the disc 2S and extends therefrom at an angle to the surface of the disc. A second glass disc 36 is sealed to the end of the ring 34 opposite the disc 23, thus forming an airtight cavity 38 between the parallelV discs 28 and 36. A thin circular layer 40 of silver,`or some other material forming a seal with the ring 34 is disposed kbetween the disc 36 and the ring 34 to provide a suitable seal. is constructed of optically-ground, flat, transparent glass.

The pins 30 and 32 extend into the cavity 38 only a short distance to form electrical contact with the electrodes to be described hereinafter. The pins 3G and 32, however, extend a substantial distance on the side of the disc 28 opposite the cavity 38, to lit within apertures 42 of a printed circuit board 44, thereby making contact with an external electric circuit.

A thin strip 46 of photoconductive material is disposed within the cavity 33 on the surface of the disc 28 in a straight line, as indicated in FIGURE 3. The photoconductve material is a composition formed by any combination of a cation material from the class consisting of cadmium, lead, indium, mercury, gallium, zinc, and aluminum, with an anion material from the group consisting of sulphur, selenium tellurium, antimony, and arsenic. A plurality of pairs of electrodes, designated 48A and 48B, are disposed partially on the disc 28 and partially on the strip 46 of photoconductive material, and the electrodes 48A and 48B on the strip 46 being spaced from each other forming agap. These electrodes 48A and 48B consist of films of electrically conducting material, such as Inconel, gold, or silver. Inconel is an alloy consisting of 80% Ni, 14% Cr, and 6% Fe.

The electrodes 43A are interconnected electrically and connected to the pin 32 by an electrically conducting strip 5t) which overlaps the electrodes 48A and the pin 32. Also, each of the electrodes 48B is connected to one of the pins 39 by an electrically conducting strip or iilm 52v which overlaps one of the electrodes 48B and one o-f the pins 30.

In one particularly suitable construction, the photoconductive strip 46 consists of cadmium selenide, and the electrodes 48A and 48B are of Inconel. In this construction, the strips 50 and 52 are of gold. It is, of course, to be understood that the electrodes 48A and the strip Si) may be of a single material and deposited as a single element, and each of the electrodes 48B and each of the strips 52 may likewise be of a single material and deposited as a single element. In the particular construction described above, the photocell assembly contains sixteen photocells 22, and thus employs Sixteen pins 30 and one pin 32.

In manufacturing the photocells according to the teachings of the present invention, the Kovar pins 30 and 32 are irst sealed within the glass disc 28 and the Kovar ring 34 sealed about the periphery of the disc 28. It is to be understood that the pins 30 and 32 may be constructed of other electrically conducting materials and the disc 28 and ring 34 of other structural materials. Glass has been employed for the disc 28 because of its electrically insulating properties, and Kovar has been employed because of its thermal advantages when used with glass. A mask 54 having a thin straight slot 56 is then disposed in contact with the side of the disc 28 confronting the outwardly extending ring 34. The assembly of disc 28, pins 30 and 32, ring 34 and mask 54 are then placed in an evacuated chamber, and alternate layers of an anion material of the class described above and a cation material of the class described above are placed on the mask and disc 28 by vaporization within the evacuated chamber as disclosed in the application entitled Semi-Conductive Films and Methods of Producing Them, referred to above. While a single layer of a cation material and a single layer of an anion material are satisfactory, it is generally desirable to provide a plurality of layers of each anion and cationl material. As an alternative, the mask of FIGURE 7 may The disc 36 be employed to place discrete lm spots on the glass substrate which are positioned to receive the electrodes 48A and 48B. Separate lm spots tend to provide better isolation between cells. The mask of FIGURE 7, designated 54A, has a single row of equally spaced openings of equal width 56A in place of the single slot 56 of FIGURE 4. Y

Following deposition of the anion and cation material, lthe mask 54 is removed leaving a ribbon of alternate layers of .anion and cation material on .the glass'd-isc. Therefore, the glass disc 28 and assembled elements are placed in a furnace or otherwise heated to produce a reaction between the anion and cation material. This reaction results in the formation of the strip 46 of photoconductive material. It is to be noted that'tem'pe'ratures of from 300 to 400 degrees centigrade are required to produce a reaction :between the cation and anion materials of the groups specified, and that this temperature must be maintained for a period of Itime to completeV the reaction. Since the glass disc 2S and the Kovarring 34 have approximately the same temperature coeflicients of l expansion, this process of forming the photoconductive strip 46 does not injure the glass disc 28.

After the Iphotoconductive strip 46 has been formed, the temperature of the assembly is reduced below 200 degrees centigrade, for example to room temperature, and

the electrically conducting strips 50 and 52 are placed on y the glass disc 28. This is accomplished by insertinga mask 58 having openings 60 and 62 Yin the shape of the strips 50 and 52, such as illustrated in FIGURE 5, adjacent to `the glass disc 28, and evaporating the electrically conducting strips 50 and 52 thereon.` The mask 5S comofthe film and assembly be maintained below 200l degrees .I centigrade at all times during the step of depositing thev electrodes 48A and 48B and thereafter. The purpose for maintaining the temperature below this limit isthat corroslon products tend 'to'form at substantial rates between the film and the electrodes at temperatures above this limit. FIGURE 6 illustrates ay mask 64 with a plurality of palrs of confronting openings 66A and 66B.vA The mask 64 is disposed `in contact with the disc 28, photoconduotlve strip 46, and electrically conducting strips 50 Iand 52, and the electrode materials for the electrodes 48A and 48B are evaporated on the mask64 and the exposed portions of the photocell assembly. It is to be understood that the electrodes 48A and 48B'may be de i posited prior to the strips 50 and 52, if so desired and also that a single mask may .be employed fordepositing the strips 50, 52, and electrodes 48A and 48B., -However, photocells requiring spacings of approximatelyOOl,

inch f or use in optical encoders, require electrodesto be deposlted 1n `two steps as illustrated in order to provide masks of suciently narrow tolerances.

The photocell assembly is then completedby sealing the glass plate 36 tothe Kovarring 34.y In order toaccompli'sh this step, a silver ring 40 is disposed about the periphery of the glass plate 36, and the ring is fused by heating the Kovar ring 34,

In one particular construction, the photocell assembly has a photoconductive strip 46 of cadmium selenide, electrodes 48A and 48B of Inconel, and connecting4 strips 50 and S2 of gold. This combination of materials has proven Y i to produce photocells ywith an improved response time over gold electrodes and other photoconductive materials.

Also, photocells constructed in -this manner have Vtheir maximum sensitivity to light of approximately 6400 angstroms which is readily produced 'by a light source.. In the manufacturing of cadmium selenide cells, two 'layers of cadmium and two ,layers of selenium are deposited on the disc 28, and then heated at a temperature of from kdepositing the electrodes.

300 to 400 degrees centigrade for a period of appro-ximately one hour. The temperature of the assembly is then reduced `to .approximately room temperature before At all times thereafter in the manufacturing process, the temperature of the assembly is maintained near room temperature, i.e. below 100 degrees centigrade.

It is olea-r from the foregoing disclosure that the photocell assembly is maintained at a relatively low temperature throughout all steps following the react-ion between the anion and cation materials which form the photo-conductive strip 46. As a result, a lower resistance contact is assured between the photoconductive strip 46 and the electrodes 48A and 48B. Further, it is also clear that only the glass dise 36 requires optical properties. Hence, the disc 28 may be selected of materials suitable to withstand the temperate ranges required in the manufacturing of photocell assemblies and materials which are readily sealed `about the pins 30 .and 32,.

It is also possible to construct photocells with photoconductive films of the .type described with the electrodes directly abutting the substrate and the pho-toconductive film overlying lthe electrodes, and such photocells when properly constructed will exhibit electrical characteristics comparable to the photocell assembly illustrated in FIG- URES 1 through 3 and 8. FIGURE 9 illustrates such a photocell assembly as a modification of the photocell assembly illustrated in FIGURES 1 through 3 and 8. Electrodes 70A and 70B are directly disposed on the glass disc 28, anda mass 72 of photoconductive material identical to that of the strip to is disposed between the electrodes 70A and 70B.

`Because of the fact that the photoc'onductive layer or strip 72 requires relatively high temperatures when being formed, it is necessary to restrict the materials for the electrically conducting electrodes 70A and 70B. Rhodium has been found to be the most desirable electrode material to date, and only two other materials have been found to be satisfactory These materials are Inconel fand electrically conducting glass, namely SnO2 glass often referred to as Nesa glass. The photoconductive layer 72 may be formed of any of the materials described above for the strip 46, and is formed in an identical manner.

It is also necessary when fabricating photocells where the electrodes are disposed on the side of the photoconducltive material opposite the direction of the light to limit the thickness of the layer of photoconductive material disposed on the confronting electrodes. If the photoconductive layer '72 is no more than lone hundred m-olecules in depth, the effective spacing between the ends o-f the electrodes 70A and 7 0B approximates the actual spacing. However, if the photoconductive layer is deposited on the ends of the electrodes to a depth in excess of one hundred molecules, the eifective spacing between the electrodes will be greater than the actual spacing.

Inconel electrodes may be deposited on the glass disc substrate in any of the conventional manners, such as employing one of the masks of FGURES 5 and 6, and evaporating a layer of Inconel onto the glass substrate. It is generally necessary to scribe or etch electrically electrically conducting glass from the glass disc 28 in order to form the electrically conducting electrodes 70A and 70B, although other means are also available to place the electrically conducting glass electrodes on the glass substrate. Rhodium electrodes may be etched upon the glass substrate in the manner disclosed in the application of the inventors entitled Methods of Etching Metals in the Platinum Group and Producing Printed Circuits Therefrom, led April 5, 1957, Serial No. 651,009, now Patent No. 3,013,956. Y

Those skilled in the art will devise applications and modifications of the photocells and assemblies and methods of making them as a result of the foregoing disclosure. It is therefore intended that the scope of the present invention be not limited by the foregoing disclosure, but rather only by the appended claims.

The invention claimed is:

l. The method of producing a photocell assembly having a plurality of photocells disposed on an axis comprising the steps of mounting a plurality of pins in a plurality of bores disposed adjacent to the perimeter of a flat glass plate-shaped base of electrically insulating material with the pins extending parallel to each other from one surface of the base and being exposed on the other surface of the base, thereafter positioning a first mask having a slot defining the axis of the photocells on the said other surface of the base, thereafter depositing alternate layers of a cation material chosen from the class consisting of cadmium, lead, indium, mercury, gallium, zinc and aluminum, and an anion material chosen from the group consisting of sulphur, selenium, tellurium, antimony, and arsenic, on the surface of the mask and exposed base, thereafter removing the first mask and heating the base and deposited layers to a temperature between 300 and 400 centigrade to produce a reaction between the anion and cation to form a semiconductive iilm, said temperature being below the melting point of the glass base, thereafter cooling the base and film to a temperature below 200 degrees centigrade, thereafter positioning a second mask having a plurality of pairs of apertures on the base, the apertures of each pair being on opposite sides of an axis and the axis of the second mask being positioned over the axis of the semiconductive hlm and each aperture of each pair confronting a portion of the semi- Vconductive film, vapor depositing an electrically conducting layer on the second mask and exposed surface of the film to form a plurality of pairs of electrodes on the surface of the semiconductive lrn and Velectrically interconnecting the electrodes and the pins.

2. rlfhe method of producing a photocell assembly having a plurality of photocells disposed on an axis comprising the steps of claim 1 wherein the step of electrically interconnecting the electrodes and the pins includes positioning a third mask on the surface of the base, semiconductive lm and electrodes, the third mask having a plurality of slots, each slot confronting a portion of an electrode and the exposed end of one of the pins, and evaporating an electrically conducting layer on the third mask, and exposed portions of the base, electrodes and pins.

3. The method of producing a photocell assembly comprising the steps of claim 2 wherein the electrically conducting material evaporated on the second mask is of the material of the class consisting of S1102 glass, rhodium, and a composition of nickel, chromium and iron.

4. The method of producing a photocell assembly comprising the steps of claim 3 wherein the material evaporated on the third mask consists of gold.

5. The method of producing a photocell assembly having a plurality of photocells comprising the steps of mounting a plurality of electrically conducting pins on a base of electrically insulating material having two opposite surfaces and a melting point above 400 centigrade, the pins extending outwardly from one surface and protruding from the other surface, positioning a rst mask having an opening therein in abutment with said other surface of the base, thereafter depositing alternate layers of a cation material chosen from the class consisting of cadmium, lead, indium, mercury, galliurn, zinc, and aluminum, and an anion material chosen from the group consisting of sulphur, selenium, tellurium, antimony, and arsenic, on the surface of the mask and exposed base, thereafter removing the first Vmask and heating the base and deposited layers to a temperature between 300 and 400 centigrade to produce a reaction between the anion and cation to form a semiconductive film, thereafter cooling the base and lilm to a temperature below 200 centigrade, thereafter positioning a second mask having a plurality of pairs of apertures on the base, each of said pairs of apertures and the portion of said second mask between 'y the apertures of each pair confronting a continuous portion of the lm and the adjacent edges of the apertures of each pair being disposed on straight parallel axes, vapor depositing an electrically conducting layer on the second mask and exposed surface of the film to form a plurality of pairs of electrodes on the surface of the semiconductive lm, removing the second mask from the surface of the base, positioning a third mask in abutment with the other surface of the base, film, and electrodes, said third mask having a plurality of slots, each slot extending between and overlapping one electrode of each pair and the exposed surface of one of the pins, and depositing a layer of electrically conducting material on the third mask, and exposed portions of the base, and electrodes.

6. The method of producing a photocell comprising the steps of claim 5, wherein the irst mask is provided with a separate opening for each photocell and a plurality of layers of cation and anion material are deposited on each area of the base exposed through the openings of said first mask, and the second mask is positioned in abutment with said other surface of the base with one pair of apertures confronting each layer of photoconductive film.

7. The method of producing a photocell assembly comprising the elements of claim 4, wherein the base of electrically insulating material is provided with a ange extending outwardly about the perimeter of said other surface in combination with the step of sealing a transparent plate to the ange confronting said other surface.

8. The method of producing a photocell assembly cornprising the elements of claim 1 in combination with the 30 References Cited by the Examiner UNITED STATES PATENTS 2,367,816 l/45 Wyss 313-94 2,634,322 4/53 Law 117-200 X 2,670,523 3/54 Orthuber 29-25.l7 2,745,047 5/56 Lighty 117-200 2,749,598 6/56 Orthuber 29-25.17 2,759,861 8/56 Collins et al. 148-15 2,763,581 9/56 Freedman 14S-1.5 2,765,385 10/56 Thomsen 117-212 2,793,275 5/ 57 Breckenridge et al 338-15 2,809,132 10/57 Bloem 117-200 2,813,991 11/57 Taft 313-94 2,865,793 12/58 De Nobel 117-200 2,892,250 6/59 Bartels 29-155.63 2,908,594 10/59 Briggs 117-201 2,916,810 12/59 Smith et al. 117-200 X OTHER REFERENCES Physical Review, vol 92, No. 6, December 1953, pages 1573-1575,

Electronic Engineering, Oct. 1, 1946, pages 316, 317 and 322.

IOHN F. CAMPBELL, Primary Examiner.

WHITMORE A. WILTZ, Examiner. 

1. THE METHOD OF PRODUCING A PHOTOCELL ASSEMBLY HAVING A PLURALITY OF PHOTOCELLS DISPOSED ON AN AXIS COMPRISING THE STEPS OF MOUNTING A PLURALITY OF PINS IN A PLURALITY OF BORES DISPOSED ADJACENT TO THE PERIMETER OF A FLAT GLASS PLATE-SHAPED BASE OF ELECTRICALLY INSULATED MATERIAL WITH THE PINS EXTENDING PARALLEL TO EACH OTHER FROM ONE SURFACE OF THE BASE AND BEING EXPOSED ON THE OTHER SURFACE OF THE BASE, THEREAFTER POSITIONING A FIRST MASK HAVING A SLOT DEFINING THE AXIS OF THE PHOTOCELLS ON THE SAID OTHER SURFACE OF THE BASE, THEREAFTER DEPOSITING ALTERNATE LAYERS OF A CATION MATERIAL CHOSEN FROM THE CLASS CONSISTING OF CADMIUM, LEAD, INDIUM, MERCURY, GALLIUM, ZINC AND ALUMINUM, AND AN ANION MATERIAL CHOSEN FROM THE GROUP CONSISTING OF SULPHUR, SELENIUM, TELLURIUM, ANTIMONY, AND ARSENIC, ON THE SURFACE OF THE MASK AND EXPOSED BASE, THEREAFTER REMOVING THE FIRST MASK AND HEATING THE BASE AND DEPOSITED LAYERS TO A TEMPERATURE BETWEEN 300* AND 400* CENTRIGRADE TO PRODUCE A REACTION BETWEEN THE ANION AND CATION TO FORM A SEMICONDUCTIVE FILM, SAID TEMPERATURE BEING BELOW THE MELTING POINT OF THE GLASS BASE, THEREAFTER COOLING THE BASE AND FILM TO A TEMPERATURE BELOW 200 DEGREES CENTRIGRADE, THEREAFTER POSITIONING A SECOND MASK HAVING A PLURALITY OF PAIRS OF APERTURES ON THE BASE, THE APERTURES OF EACH PAIR BEING ON OPPOSITE SIDES OF AN AXIS AND THE AXIS OF THE SECOND MASK BEING POSITIONED OVER THE AXIS OF THE SEMICONDUCTIVE FILM AND EACH APERTURE OF EACH PAIR CONFRONTING A PORTION OF THE SEMICONDUCTIVE FILM, VAPOR DEPOSITING AN ELECTRICALLY CONDUCTING LAYER ON THE SECOND MASK AND EXPOSED SURFACE OF THE FILM TO FORM A PLURALITY OF PAIRS OF ELECTRODES ON THE SURFACE OF THE SEMICONDUCTIVE FILM AND ELECTRICALLY INTERCONNECTING THE ELECTRODES AND THE PINS. 